It is known practice to dye human keratin fibers, such as the hair, with dye compositions comprising oxidation dye precursors, which are generally known as oxidation bases and couplers. These oxidation bases and couplers are colorless or weakly colored compounds, which, when combined with oxidizing agents such as peroxides, for example, hydrogen peroxide, give rise to colored compounds by a process of oxidative condensation.
The colorations resulting therefrom are permanent, strong, and resistant to external agents, such as light, bad weather, washing, perspiration, and/or rubbing. This process, which is generally applied at basic pH, makes it possible simultaneously to dye and lighten the fibers, which is reflected in practice by the possibility of obtaining a final coloration that is lighter than the original color. In addition, lightening of the fiber may have the advantageous effect of generating a unified color in the case of grey hair, and of bringing out the color, i.e., making it more visible, in the case of naturally pigmented hair.
It is also known practice to dye human keratin fibers with a direct dye. The process conventionally used in direct dyeing comprises applying direct dyes to the keratin fibers, which are colored and coloring molecules that have affinity for the fibers, leaving the dyes on the fibers, and then rinsing the fibers.
It is known practice, for example, to use direct dyes chosen from nitrobenzene, anthraquinone, nitropyridine, azo, xanthene, acridine, azine, and triarylmethane direct dyes.
The colorations resulting therefrom are particularly chromatic colorations, but are, however, temporary or semi-permanent since the nature of the interactions linking the direct dyes to the keratin fiber, and their desorption from the surface and/or core of the fiber are generally considered responsible for their poor dyeing power and their poor fastness with respect to washing and/or perspiration. These direct dyes are also generally light-sensitive due to the poor resistance of the chromophore with respect to photochemical attack, and often lead, over time, to fading of the coloration of the hair. In addition, their light-sensitivity is dependent on their uniform distribution or their distribution as aggregates in the keratin fiber.
The direct dyes may be combined with oxidizing agents. However, the direct dyes are often sensitive to the action of oxidizing agents and reducing agents, which makes them generally difficult to use in lightening direct dyeing compositions based on aqueous hydrogen peroxide solution and based on a basifying agent, or in oxidation dye compositions in combination with precursors such as oxidation bases or couplers.